The present invention relates generally to gas turbine engines, and, more specifically, to turbine blade cooling.
In a gas turbine engine, air is pressurized in a compressor and mixed with fuel and ignited in a combustor for generating hot combustion gases. The gases flow downstream through turbine stages which extract energy therefrom for powering the compressor and producing useful work, such as powering a fan for propelling an aircraft in flight.
Turbine stator vanes and rotor blades include corresponding hollow airfoils through which air bled from the compressor is circulated as a coolant therefor. The airfoils may include one or more cooling circuits therein extending radially or longitudinally for channeling the coolant. Various features may be incorporated for increasing heat transfer for more efficiently cooling the airfoils.
Each airfoil has a generally concave pressure sidewall and an opposite generally convex suction sidewall joined together at axially opposite leading and trailing edges. The combustion gases flow downstream over the two sidewalls with different amounts of heat input or load therein. Accordingly, the internal cooling circuits are specifically configured to match the different cooling demands of the airfoil for improving efficiency of operation.
The coolant is discharged from the airfoil through various apertures, such as film cooling holes disposed in longitudinal rows or columns along the pressure and suction sidewalls, and a column of trailing edge apertures or slots. These various apertures are small in size and configured for locally cooling the airfoil in their vicinities.
The coolant is discharged from the apertures with a minimum backflow margin to prevent ingestion of combustion gases therein, and a corresponding blowing ratio is limited at each aperture to prevent undesirable discharge jets therefrom.
The discharge of the coolant through the apertures affects the cooling ability thereof as well as affects overall efficiency of the engine since the coolant mixes with the combustion gases flowing over the airfoil for subsequent discharge from the engine. Differences in direction and velocity of the discharge coolant and the combustion gases cause undesirable mixing losses which should be minimized.
Furthermore, the coolant bled from the compressor may include fine particles of dust which travel through the airfoil with the coolant and discharged therewith through the apertures. Since the apertures are small, it is undesirable to accumulate dust therein which would further reduce their size or interrupt coolant flow therethrough which would adversely affect the desired cooling.
Accordingly, it is desired to provide a turbine airfoil having improved cooling resistant to dust accumulation in the discharge apertures thereof.